Q18 of 284 Page 261

The optician's prescription for a spectacle lens is marked+ 0.5 D. What is the: (a) nature of spectacle lens?

(b) focal length of spectacle lens ?

(a) nature of spectacle lens is Convex lens

(b) Power of a lens = +0.5 D


P = 1/f


f = 1/P = 1/(+0.5) = +2 m


Focal length is 2 m.


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